“Enough is enough. I should not have to submit to a digital strip search or being groped by a glorified security guard," writes commenter vrwc1 in a typical post on cnet.com. "This is the largest violation of personal privacy we've ever seen.”

The choice to get on an airplane, the argument goes, is not probable cause for such invasive searches, nor does buying a ticket constitute consent to be subjected to a “virtual strip search” and “groping,” as critics call the two searches.

“Are the conditions that you’re consenting to so draconian and so unreasonable that there’s a Fourth Amendment problem?” asks William Schroeder, a professor of law at Southern Illinois University at Carbondale. “I don’t think that argument is going to carry the day, given that people have hidden bombs on their bodies in ways that cannot be found through less invasive searches.”

'You don't have to fly'

At the heart of the issue is consent, says Professor Schroeder. Have people consented to this search, simply by buying a ticket? "I certainly understand why people are not altogether pleased about it,” says Schroeder, but “you’ve consented. You don’t have to fly – that’s your choice.”

Others, however, suggest that the searches overreach. In order to pass the Supreme Court’s test for constitutionality, searches must balance a “reasonable” amount of privacy invasion against the likelihood of finding evidence of a crime.

The "costs" of the scans have been reported from every corner of the Internet. Stories are emerging of TSA officers commenting inappropriately on scans, and of passengers reporting their pat-downs as “sexual assault.”

What is not yet clear are the benefits.

John Pistole, head of the TSA, told a Senate committee Tuesday that pat-down techniques are so thorough that they would have detected the explosives concealed in the underwear of Umar Farouk Abdulmutallab on Christmas Day last year.

“It’s more invasive than I’m used to,” acknowledged Mr. Pistole, when asked by Sen. Byron Dorgan (D) of North Dakota if he had received an enhanced pat-down himself, during a Wednesday morning hearing of the Senate Commerce, Science, Transportation Committee.

After acknowledging his own personal discomfort with the search, Pistole stood by the procedure as a screening technique. “The bottom line is, we need to provide for the best possible security,” he said.

Do full-body scanners work?

But the value of the full-body scans, which are used 50 times more often than the pat-downs, are less certain.

Italian security officials stopped using the scanners in September. "We didn't get good results from body scanners during testing,” said Vito Riggio, the president of Italy’s aviation authority, describing the scans as slow and ineffective.

British scientists found that the scanners picked up shrapnel and heavy wax and metal, but missed plastic, chemicals and liquids, reported UK newspaper The Independent in January.

“Some of these technological responses to terrorism really start to seem like placebos,” says Susan Herman, President of the American Civil Liberties Union (ACLU) and law professor at Brooklyn Law School. “To the extent that people understand what the benefits are, and the invasion of privacies are, they can make more informed decisions about giving up their privacy for machines that make them feel better, but don’t do the job of preventing any terrorist device from getting on an airplane.”

“This technology can go right up a woman’s skirt," and it can reveal medical conditions via the presence of an adult diaper, a colostomy bag, or other personal medical equipment – information that individuals have the right to keep private, she adds.

The TSA has relented in the face of some complaints. It announced Tuesday that it will no longer screen children under 12.

Chris Calabrese, a privacy lobbyist for the ACLU, says “the balance seems to be missing here.”

“Until it’s restored, I think TSA is going to continue to hear these concerns," he adds. "This is pretty far outside the norm of what people expect when they travel, even in these days. We’ve certainly seen the normal shift over the past decade, but there’s still a line, and both these procedures are on the wrong side of that line.”